Mature leaf is a different tissue, not a worse one
A leaf that has finished expanding has thicker cell walls, more structural carbohydrate and lignin, a harder cuticle and a lower share of the soluble compounds that dominate a young shoot. It is also the plant’s working photosynthetic apparatus, which is why the layer of it under the plucking table is left in place. When it is harvested deliberately, the material behaves differently in every processing step: it withers more slowly because there is less water to lose relative to its mass and the cuticle resists losing it, it resists rolling, it needs more heat and longer to fix, and it gives an infusion that is lower in bitterness and astringency and flatter in aroma. Those are not defects. They are the properties a category may want. The mistake worth naming is treating leaf age as a single quality axis with young at the top. Leaf age is a variable that has to be matched to a process, in the same way that grape ripeness or milk fat content is, and a process designed around mature leaf performs badly when given fine shoots.
Where mature leaf is the specification
Japanese bancha is made from later-season and larger leaf and is a different tea from sencha rather than a lesser one; it is milder, lower in caffeine and drunk in quantity. Chinese dark teas require mature leaf and stem because the months of piling, microbial activity and pressing they undergo need material with enough structure to survive it — a fine bud-and-leaf pick would disintegrate. Compressed brick teas made for the historic Tibetan and Mongolian trade were built on coarse material by design, since the requirement was durability, volume and a strong infusion that stands up to butter, milk and salt. Liu Bao, Fu brick and the Sichuan and Hunan bricks all sit here. Lower-grade material also feeds two enormous modern industries that rarely admit it: the teabag trade and iced-tea manufacture both use leaf that fine-tea vocabulary would call coarse, and both make products that are competent at what they are for. The category error is judging them against a standard they are not attempting.
Stem and stalk are not leaf at all
Stem is a distinct tissue with a distinct composition, and treating it as a contaminant misses what it does. It carries a different balance of soluble compounds from leaf — notably a higher share of the amino acids associated with sweetness relative to the polyphenols associated with astringency — which is why teas made deliberately from stem taste sweet and mild rather than merely weak. Japanese kukicha is made from the stems and stalks separated during sencha and gyokuro sorting; karigane is the same idea from higher-grade material, and stems from shaded leaf carry the shaded character with them. Roasted, the same material becomes stem hojicha. The point worth taking is that these are by-products in the sense that they arise from sorting another product, and not in the sense of being residue. Karigane from a good gyokuro sorting line is expensive and is bought on purpose. A whole small category exists because somebody noticed that the part being discarded was interesting.
Stem in Chinese and pu-erh practice
Chinese practice regards stem differently again. In sheng pu-erh a proportion of stem is generally regarded as desirable rather than tolerated, on the reasoning — widely held among producers and not, so far as TeaHQ can establish, formally demonstrated — that stem contributes to how a cake ages and to how well a compressed tea breathes. Compression is the practical part of that: a cake of pure fine bud material presses very densely, and stem gives it structure and air. In Wuyi and Anxi oolong, stem is removed after processing rather than avoided during picking, because the shoot has to be picked open and mature for the process to work and the stalk is only a nuisance at the end. Elsewhere, sorting stem out is straightforwardly a grading operation: Indian and Sri Lankan grade letters penalise stalk, sorting machinery is built to extract it, and a stalky orthodox grade sells for less. Three traditions, three different attitudes, one plant part.
Huang pian, and the leaf that is sorted out
Yunnan practice has a name for the yellowed, oversized leaves picked out during the sorting of maocha: huang pian, yellow flakes. They are the mature leaves that came along with the shoots and are removed because they will not roll and will look wrong in a finished cake. They are also sold, loose or lightly pressed, and drunk for a sweet, soft, low-astringency infusion that behaves quite unlike the tea they were sorted out of. It is a good illustration of the general point: the same material is a defect in one product and a product in another, and the difference is entirely a decision about what is being made. What follows for a reader is a small piece of scepticism about grading vocabulary. Terms like broken, coarse, stalky and flaky are descriptions of physical material relative to a target, and the target is set by a market. They are not measurements of anything intrinsic, and a tea that is off-grade in one system may be exactly on specification in another.
What this changes about reading a tea
Three practical consequences. First, a tea made from coarse material and priced low is not necessarily badly made, and a tea made from fine material and priced high is not necessarily well made — plucking standard sets the material cost and says little about the skill applied after it. Second, categories built on mature leaf and stem should be judged on their own terms: a bancha that tastes like a weak sencha is a poor bancha, and one that tastes clean, light and slightly woody is doing its job. Third, the presence of stem in a wet leaf is information rather than a verdict, and what it tells you depends on which tradition made the tea. There is also a quiet economic point. Fine plucking removes a small fraction of what a bush produces, and the rest of the plant’s growth still exists and still has to go somewhere. Much of the world’s tea by volume is made from that remainder, and a catalogue that only describes the top of the shoot is describing a small minority of the crop.